A typical conventional liquid hydrogen (LH2) production process can be separated into three steps: (1) gaseous hydrogen production; (2) separating hydrogen from a gaseous mixture; and, (3) liquefying gaseous hydrogen to liquid hydrogen (LH2). As shown in FIG. 1, LH2 production begins with the well-known Steam Methane Reforming (SMR) process, in which a gas mixture containing carbon monoxide (CO), carbon dioxide (CO2), water and methane residues are mixed together with hydrogen in a Steam Methane Reformer to produce hydrogen (H2) rich gas. The hydrogen (H2) rich gas mixture is then separated through several pairs of adsorption columns in a purification process called Pressure Swing Adsorption (PSA). About 85% of the hydrogen produced is then liquefied into LH2, with purity ranging from 99.90 to 99.99%. The remaining 15% of hydrogen, together with remaining CO and methane (CH4), are burned in an incinerator to produce CO2 and water, yielding 11.8 kg of CO2 per 1 kg of hydrogen (H2) produced through this process.
The disadvantages of the Pressure Swing Adsorption (PSA) process include, but are not limited to, low process efficiency, low hydrogen recovery from a gas mixture, and the production of off-gases, containing high concentrations of carbon monoxide (CO); H2 and methane (CH4) that are generally burned to recover only the fuel value of the combustible gases, thereby wasting CH4 and CO as H2 production components. Another disadvantage of PSA systems related to the level of hydrogen purity obtainable. Normally, H2 purity greater than 99.9995% is required for use in aerospace, as a space travel propellant. In case of hydrogen fuel cells, such applications do not tolerate contaminants such as carbon monoxide (CO) and hydrocarbons at levels exceeding a few parts per million (ppm), because the contaminants poison the platinum catalysts utilized in fuel cells. Thus, GH2 production through PSA purification alone cannot meet high purity standards. In order to do so an H2 purification procedure must be accomplished prior to the liquefaction.
The present invention provides methods, systems and devices that overcome the disadvantages of the conventional process shown in FIG. 1. Five embodiments of the invention have been developed through the use of the chemical engineering simulation tools HYSYS™ and Aspen Plus™ to determine the process efficiencies and to calculate CO2/H2 ratios.